Cation disordering in magnesium aluminate spinel crystals induced by electron or ion irradiation

Structural changes in magnesium aluminate spinel (MgO · nAl2O3) single crystals, which were irradiated with 900 keV electrons or 1 MeV Ne+ ions at 873 K, were examined by electron channeling enhanced X-ray microanalysis. Unirradiated MgO · Al2O3 has a tendency to form the normal spinel configuration, where Mg2+ ions and Al3+ ions occupy mainly the tetrahedral and the octahedral sites, respectively. Electron irradiation induces simple cation disordering between the tetrahedral sites and the octahedral sites in MgO · Al2O3. In addition to cation disordering, slight evacuation of cations from the tetrahedral sites to the octahedral sites occurs in a peak-damaged area in MgO · Al2O3 irradiated with Ne+ ions. In contrast, cation disordering is suppressed in MgO · 2.4Al2O3 irradiated with electrons. The structural vacancies, present in the non-stoichiometric compound, appear to be effective in promoting irradiation damage recovery through interstitial–vacancy recombination.